Spark Plasma Sintering (SPS) of NASICON Ceramics

Spark plasma sintering (SPS) method was used to obtain dense NASICON ceramics with a high-electrical conductivity, which was compared with conventional solid-state sintering. The fully dense NASICON was achieved at a relatively low-sintering temperature of 1100°C, whereas the apparent density of the specimen prepared by conventional sintering was 74% of the theoretical density. The highest conductivity of 1.8 × 10⁻³ Scm⁻¹ at 25°C, which is comparable to the best value reported, was achieved using the SPS process. Considering the phase, density, and microstructure, it appears that there is more room for improved conductivity by controlling the amount of monoclinic zirconia and the resistive grain-boundary glass phase.     

Sintering of a sodium-based NASICON electrolyte: A comparative study between cold,field assisted and conventional sintering methods

Scandium-substituted NASICON (Na_3.4Sc_0.4Zr_1.6Si₂PO₁₂) is a promising electrolyte material for sodium-ion solid state batteries, with the highest ionic conductivity reported to date for a NASICON material. Low-temperature densification and control of microstructure are important factors to enable the low-cost manufacturing of such new battery type. Non-conventional sintering techniques such as Field Assisted Sintering Technology / Spark Plasma Sintering (FAST/SPS) and Cold Sintering are therefore investigated and compared to conventional free sintering. FAST/SPS enables to get rapidly dense samples (99% TD) at lower temperatures than the ones required by conventional sintering routes and with similar electrical properties. Cold sintering experiments, involving the addition of aqueous solutions as sintering aids and high mechanical pressure, enable a moderate densification, but at temperatures as low as 250 °C. Further heat treatments still below the conventional sintering temperature increased the achieved density and ionic conductivity.     

Full Activation of Mn4+/Mn3+ Redox in Na4MnCr(PO4)3 as a High‐Voltage and High‐Rate Cathode Material for Sodium‐Ion Batteries

Developing high‐voltage cathode materials is critical for sodium‐ion batteries to boost energy density. NASICON (Na super‐ionic conductor)‐structured Na_xMnM(PO₄)₃ materials (M represents transition metal) have drawn increasing attention due to their features of robust crystal framework, low cost, as well as high voltage based on Mn⁴⁺/Mn³⁺ and Mn³⁺/Mn²⁺ redox couples. However, full activation of Mn⁴⁺/Mn³⁺ redox couple within NASICON framework is still a great challenge. Herein, a novel NASICON‐type Na₄MnCr(PO₄)₃ material with highly reversible Mn⁴⁺/Mn³⁺ redox reaction is discovered. It proceeds a two‐step reaction with voltage platforms centered at 4.15 and 3.52 V versus Na⁺/Na, delivering a capacity of 108.4 mA h g^?1. The Na₄MnCr(PO₄)₃ cathode also exhibits long durability over 500 cycles and impressive rate capability up to 10 C. The galvanostatic intermittent titration technique (GITT) test shows fast Na diffusivity which is further verified by density functional theory calculations. The high electrochemical activity derives from the 3D robust framework structure, fast kinetics, and pseudocapacitive contribution. The sodium storage mechanism of the Na₄MnCr(PO₄)₃ cathode is deeply studied by ex situ X‐ray diffraction (XRD) and ex situ X‐ray photoelectron spectroscopy (XPS), revealing that both solid‐solution and two‐phase reactions are involved in the Na⁺ ions extraction/insertion process.     

NASICON纳米晶固体材料的制备与烧结致密化

以常规无机试剂和含硅有机试剂为原料，采用溶胶-凝胶过程与压制成型烧结相结合的方法制备了NASICON纳米晶固体材料，利用TG—DTA对前驱凝胶原粉进行了分析测试，结果表明，NASICON相结构的形成温度范围为750-890℃．实验中重点对800-1000℃烧结所得纳米晶材料进行了表征．目的产物的XRD、FT—IR、FE—SEM、IS结果以及阿基米德法致密度测量结果显示，采用合适的烧结温度和周期可以成功制备出具有纳米级颗粒尺寸、良好结晶特性和较高致密度的固体电解质NASICON材料．材料电学特性测试结果表明，所制备的纳米晶固体电解质材料具有良好的离子导电特性和合理的离子传导激活能，其复合电导与温度倒数的Arrhenius图具有很好的线性关系，并且具有较高结晶特性的材料显示出更高的离子电导率．     

固体电解质CO2传感器的研究与进展

采用溶胶-凝胶法制备NASICON粉体材料，并利用XRD和IR对制得的材料进行表征。以NASICON粉体材料为基体，Li2CO3-BaCO3复合盐为敏感电极制作管式CO2气体传感器，并对其灵敏度、选择性和耐水性进行测量。在敏感电极中掺入质量分数为10%的SiO2，不仅明显改善器件的耐水性，而且使器件的初始稳定时间从30min减小到5min。     

溶胶-凝胶法合成NASICON快离子导体材料

采用以无机盐为基础的新型溶胶－凝胶法合成了NASICON快离子导体材料，在其它原料相同的情况下，分别采用硝酸和草酸作为回溶剂和原溶液酸度调节剂合成了NASICON材料，利用XRD等分析测试手段对合成产物进行了对比研究，对两种酸在反应温度和相结构的影响情况进行了讨论。     

Increase ionic conductivity of a Zn2+/F− synergy Na3Zr2Si2PO12 solid electrolyte for sodium metal batteries

Na₃Zr₂Si₂PO₁₂ (NZSP) solid-state electrolyte is considered one of the most promising solid-state electrolyte because of their excellent electrochemical and thermal stability. Even though, the low conductivity of NZSP solid-state electrolytes hinders practical application. Therefore, an anions/cations co-assisting strategy is proposed by introducing the Zn²⁺ and F⁻. The influence of adding different amounts of Zn²⁺ and F⁻ on the Na⁺ conductivity of NZSP was investigated computationally and experimentally. The Zn²⁺/F⁻ co-assisting (Na_3.3Zr_1.85Zn_0.15Si₂PO₁₂) solid-state electrolyte exhibits the ionic conductivity of 0.722 mS cm⁻¹ at 30 °C, and the activation energy of ∼0.237 eV. Its applicability in a solid-state battery is tested, and the assembled Na/Na₃V₂(PO₄)₃ (NVP) battery exhibits an outstanding electrochemical performance of 98.4% capacity retention after being cycled at 0.5 C. Moreover, DFT calculations also have been used to demonstrate the effect of doping on the crystal structure and space migration energy barrier. This research provides new ideas for improving the electrochemical properties of inorganic solid electrolytes.     

NASICON固体电解质NH_3传感器的研制

本文介绍了一种管式结构的固体电解质NH,传感器.该传感器是将溶胶-凝胶法制备的NASICON为导电层材料,以掺杂C的Cr2O3为辅助电极材料制得的.当工作温度在250～450℃时,器件对浓度为(50-500)x10-6的NH3表现出了良好的气敏性能,器件电动势EMF值与NH3浓度的对数表现出了很好的线性关系,在350℃时,器件的灵敏度为89 mV/decade.同时,器件表现出较快的响应恢复速度,对50×10-6的NH3的响应恢复时间分别为30s和60s,且有较好的选择性.     

Fast Potassium Storage in Hierarchical Ca0.5Ti2(PO4)3@C Microspheres Enabling High‐Performance Potassium‐Ion Capacitors

Hybrid potassium‐ion capacitors (KICs) show great promise for large‐scale storage on the power grid because of cost advantages, the weaker Lewis acidity of K⁺ and low redox potential of K⁺/K. However, a huge challenge remains for designing high‐performance K⁺ storage materials since K⁺ ions are heavier and larger than Li⁺ and Na⁺. Herein, the synthesis of hierarchical Ca_0.5Ti₂(PO₄)₃@C microspheres by use of the electrospraying method is reported. Benefiting from the rich vacancies in the crystal structure and rational nanostructural design, the hybrid Ca_0.5Ti₂(PO₄)₃@C electrode delivers a high reversible capacity (239 mA h g^?1) and superior rate performance (63 mA h g^?1 at 5 A g^?1). Moreover, the KIC employing a Ca_0.5Ti₂(PO₄)₃@C anode and activated carbon cathode, affords a high energy/power density (80 W h kg^?1 and 5144 W kg^?1) in a potential window of 1.0–4.0 V, as well as a long lifespan of over 4000 cycles. In addition, in situ X‐ray diffraction is used to unravel the structural transition in Ca_0.5Ti₂(PO₄)₃, suggesting a two‐phase transition above 0.5 V during the initial discharge and solid solution processes during the subsequent K⁺ insertion/extraction. The present study demonstrates a low‐cost potassium‐based energy storage device with high energy/power densities and a long lifespan.     

The crystal structure of a nonstoichiometric NASICON

The crystal structure of a nonstoichiometric NASICON prepared from a hydrothermally synthesized precursor phase was solved by means of X-ray powder and neutron powder diffraction methods. The NASICON phase is monoclinic with unit cell parameters, from Rietveld refinement of the neutron data, of a = 15.6209(8), b = 9.0326(5), $\text{c}\text{= 9.2172(5)}\text{A}\text{?}$, β = 123.67(1)°, $\text{V}\text{= 1082.5}\text{A}\text{?}{}^3$. The space group is C2/c with Z = 4. The structure is essentially that proposed earlier by Hong, but the nonstoichiometry results from replacement of part of the Zr⁴⁺ by Na⁺. Refinement of site occupancies coupled with the requirement of overall charge balance yields the formula Na_2.88(Na_0.32Zr_1.68)Si_1.84P_1.16O_11.54 which also agrees well with analytical data. Only 20% of the Na1 sites are occupied, but 80% of the Na3 sites are filled. This structure provides a framework from which to rationalize the many reports in the literature that NASICON can only be prepared with difficulty by high temperature solid state reactions.